Priority is claimed to Patent Application Number 2001-7846, filed in the Republic of Korea on Feb. 16, 2001, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor laser diode, and more particularly, to a semiconductor laser diode which can control modes of a laser by a method of controlling the width of a carrier inflow path.
2. Description of the Related Art
Semiconductor laser diodes are widely used as devices for transmitting data at a high speed or recording and reading data at a high speed in communications or players in which optical disks are used. This is because the semiconductor laser diodes can be downsized, and have a lower threshold current for laser oscillation than general laser systems.
As semiconductor laser diodes are applied in a wide variety of areas, there is an increasing need for semiconductor laser diodes which easily control smaller modes and have low threshold current for laser oscillation. As a result, semiconductor laser diodes where threshold current is reduced have appeared or are appearing. FIG. 1 shows an example of these semiconductor laser diodes.
FIG. 1 is a cross-sectional view of a semiconductor laser diode, according to the prior art, which is a ridge-shaped semiconductor laser diode having a ridge for reducing threshold current for laser oscillation and stabilizing modes. The semiconductor laser diode according to the prior art will be briefly described with reference to the FIG. 1. An n-GaN layer 12 is formed on a sapphire substrate 10. The n-GaN layer 12 may be divided into a first region R1 and a second region R2. An n-AlGaN/GaN layer 24, an n-GaN waveguide layer 26, an active layer (InGaN layer) 28, a p-GaN waveguide layer 30, and a p-AlGaN/GaN layer 32 are sequentially formed on the first region R1. Refractive indexes of the n-AlGaN/GaN layer 24 and the p-AlGaN/GaN layer 32 are lower than refractive indexes of the n-GaN waveguide layer 26 and the p-GaN waveguide layer 30 which are lower than a refractive index of the active layer 28. The p-AlGaN/GaN layer 32 has a ridge shape where the upper center protrudes. The protruding ridge of the p-AlGaN/GaN layer 32 defines a resonant region for laser oscillation on the active layer 28 by controlling current supplied. A p-GaN layer 34 is formed on the protruding ridge of the p-AlGaN/GaN layer 32. The whole surface of the p-AlGaN/GaN layer 32 is covered with a protective layer 36. A portion of both sides of the p-GaN layer 34 except for the central portion of the p-GaN layer 34 which is a path for current contacts the protective layer 36. A p-type electrode 38, which contacts the whole surface of the p-GaN layer 34, is formed on the protective layer 36.
The second region R2 of the n-GaN layer 12 where an n-type electrode 40 is formed is lower than the first region R1.
As described above, in the semiconductor laser diode according to the prior ar, supplied current is controlled due to a ridge structure to define a resonance width. Thus, there are advantages in that optical modes of the ridge structure are improved to some extent compared to an existing non-ridge structure and threshold current for laser oscillation is reduced. However, there is a problem in that multi-mode oscillation occurs depending on the width of the ridge. This problem is solved to some extent by reducing the width of the ridge to a few micrometers using a fine (or micro-machining) process. However, this machining process is not stable and it is difficult to incorporate into a mass production scheme. As shown in FIG. 2, in the semiconductor laser diode according to the prior art, a near field pattern is seriously deformed depending on the width of the ridge. Also, a switching in a lasing state may be modulated to current over or less than the threshold current. This modulation may cause deterioration of the stability of the semiconductor laser diode and shortening of the life of the semiconductor laser diode.
To solve the above-described problems, it is an object of the present invention to provide a semiconductor laser diode which can control modes of a laser and switching of a lasing state by controlling the width of a carrier inflow path from a ridge to an active layer.
Accordingly, to achieve the object, there is provided a semiconductor laser diode having a p-type material layer, an active layer, and an n-type material layer for lasing between a p-type electrode and an n-type electrode, the semiconductor laser diode comprising a carrier inflow width controller for controlling the width of a path of carriers flowing from the p-type electrode which restrictively contact the p-type material layer into the active layer. The p-type electrode restrictively contacts the p-type material layer.
The carrier inflow width controller is a first carrier inflow width controller formed on the p-type material layer not to contact the p-type electrode.
A second carrier inflow width controller is further included between the p-type material layer and the p-type electrode. Here, the second carrier inflow width controller is a ridge in which a portion of the p-type material layer protrudes toward the p-type electrode.
The p-type electrode extends over the first carrier inflow width controller and is filled with a dielectric layer. Here, the second carrier inflow width controller is a portion of the p-type electrode which protrudes down toward the p-type material layer.
The first carrier inflow width controller is a metallic pad layer using a schottky contact characteristic according to which a reverse voltage is applied when a voltage for lasing is applied.
A dielectric layer is further included between the metallic pad layer and the p-type material layer.
As described above, the semiconductor laser diode according to the present invention includes a carrier inflow width controller to control the width of a path of carriers flowing from a ridge into an active layer. Thus, even in a case where the physical width of the ridge is wide, an effective width of the ridge can be narrowed by controlling a reverse voltage applied to the carrier inflow width controller. As a result, it is possible to control modes of a laser closely related with the effective width of the ridge. Thus, even in the case where the physical width of the ridge is wide, the effective width of the ridge is controlled easily that has an advantage of mode stability. Finally, a near field pattern near to an ideal shape is obtained. Thus, the difference between horizontal and vertical shapes of the near field pattern is reduced to reduce distortion of the near field pattern. In addition, the diffusion of carriers in a horizontal direction when carriers pass through the ridge 62a is reduced, thereby reducing threshold current required for lasing. Also, the inflow path of carriers is completely blocked by increasing the reverse voltage applied to the carrier inflow width controller. Thus, rapid on/off switching can be realized. As described, it is easy to modulate the semiconductor laser diode without changing threshold current. Thus, the stability of the semiconductor laser diode can be ensured and the life of the semiconductor laser diode can be extended. As described above, the effective width of the ridge is controlled regardless of the physical width of the ridge. Thus, a process margin for the ridge is wide in a process of manufacturing the semiconductor laser diode. Therefore, a process of manufacturing the semiconductor laser diode is simple compared to the prior art and yield can be increased.